Matchable low-E I.G. units and laminates and methods of making same

ABSTRACT

A neutral blue-green heat treatable and matchable glass laminate or I.G. unit employs a layer system whose visible transmittance increases by at least 4% during heat treatment and whose ΔE* ab  is less than about 3.0 and Δa* is less than about 0.7. The sputter coated layer system includes a silver layer sandwiched between nichrome layers and thereafter layers of Si 3 N 4 .

[0001] This invention relates to insulating glass units and laminateshaving sputter-coated layer systems thereon. More particularly, thisinvention relates to such articles which are heat treatable and arematchable with their unheat treated counterpart.

BACKGROUND OF THE INVENTION

[0002] In U.S. Pat. No. 5,688,585 (having overlapping inventorshipherewith) there is disclosed a significant step forward in the art ofcoating glass sheets used for solar management purposes which must bematchable in appearance after heat treatment with their unheat treatedcounterpart. In this patent it was accurately reported that, for thenon-silver containing layer systems of that invention, if ΔE wasmaintained below a certain minimal value no greater than about 2.0, theheat treatable, non-silver containing layer systems therein would bematchable. The subject invention constitutes an improvement upon theinvention of the aforesaid '585 patent.

[0003] In contrast to the '585 patent, the subject invention hereinprovides a silver containing layer system which avails itself of thesolar management advantages of silver. By the discovery that if certainparameters in addition to ΔE are maintained within certain limits, asdescribed below, it has now been surprisingly found that silver inrather substantial thicknesses may be employed while still achievingheat treatability and matchability if the layer systems are employed ineither insulating glass units (I.G. units) or laminates (or othersimilar articles having two or more light transmitting substrates ofglass). It is understood, of course, that a noncoated substrate ascontemplated herein may be either glass or an equivalent thereof, suchas a transparent plastic material. Moreover, it is a further discoveryof this invention that matchability in such articles is achievable eventhough the coated monolithic glass substrate employed, while heattreatable, is not in and of itself matchable.

[0004] The need for matchability is well known in the glass window, doorand windshield arts, as is the need for heat treatability. Glasssubstrates, normally sheet glass used for windows, doors, etc. are oftenproduced in large quantities and cut to size in order to fulfill theneeds of a particular situation such as a new multi-window and dooroffice building. It is not only desirable in these buildings, but oftena necessity in order to conform to various code provisions, that some ofthe windows and doors be heat treated (i.e. tempered, heat strengthenedor bent) while others, principally to save money, need not be, and thusare not heat treated. Still further, such buildings often employ I.G.units and/or laminates for safety and/or thermal control. Obviously theunits and/or laminates which are heat treated must match with (i.e.appear in color, and preferably in transmittance and reflectance aswell, to be substantially the same as) the unheat treated I.G. unitsand/or laminates used together in the building, for architectural andaesthetic purposes. In addition, currently, such windows, doors, etc.for many commercial purposes should preferably be of a substantiallyneutral color, preferably tending to the blue-green side of thespectrum.

[0005] Through rigorous trial and error attempts, it has in the pastbeen possible to achieve matchability in systems other than those of theaforesaid '585 patent but only between two different layer systems, oneof which is heat treated and the other is not. The necessity ofdeveloping and using two different layer systems to achieve matchabilitycreates additional manufacturing expense and inventory needs which areundesirable. The aforesaid invention disclosed in the '585 patentfulfilled a definite need in the art which overcame this problem.However, it could not, in that system, take advantage of the use ofsilver for its known IR reflectance properties, and still achieve itsdesired results.

[0006] The silver containing layer systems of the invention herein areuseful in glass articles which generically may be described as anarticle or structure which includes at least two glass substrates inlight transmitting relationship with each other. Preferred articlesinclude architectural doors and windows, such as laminates and I.G.units, as well as, at times automotive windshields and windows.

[0007] As used herein, the term I.G. unit is synonymous with the term“insulating glass unit” and is used according to its conventional andwell known meaning in the art. FIGS. 2 and 4 illustrate, schematically,a typical I.G. unit contemplated for use with the coating systems ofthis invention. Generally speaking, as contemplated herein, I.G. unitsare comprised of two or more parallel, spaced sheets of glass held inspaced relationship by an appropriate frame structure. The space(s)between the two or more sheets, typically about one-half inch, eitherhas air in it or an inert gas such as argon, or is partially evacuated.Most are provided with a desiccant within the space to prevent“fogging.” It is, of course, understood that FIGS. 2 and 4 are merelyexamples of many types of I.G. units used for thermal and/or soundinsulation purposes, as contemplated by this invention.

[0008] The term “laminate” is also well understood in the glass art andis used herein according to its well known meaning. Glass laminatesnormally include two or more unspaced substrates of glass (shaped orunshaped sheets of glass) which, in the instances of this invention willhave at least one coating of a layer system of this invention thereon,normally but not always located at the interface of the two sheets. Suchlaminates may be flat structures (e.g. sheets cut to size) used inwindows, doors or windshields, or bent to meet specific architectural orautomotive needs. For example, FIG. 5 schematically illustrates, ingeneric fashion, a typical two sheet (pane) laminate used as a curvedwindow or windshield.

[0009] By way of further background related to this invention attentionis directed to the discussion of the prior art in the aforesaid '585patent. With respect thereto, the BOC Group, Inc. (Wolfe et al) as wellas two of the inventors hereto (Messrs. Larson and Lingle) for GuardianIndustries, and others have hereto reported various layer coating system(some commercial) employing metallic silver sandwiched between layers ofnichrome followed by layers of Si₃N₄ to achieve either heat treatable ornonheat treatable solar management coating systems. Other examples ofsuch a structure by these inventors include U.S. Pat. Nos. 5,344,718;5,376,455; 5,514,476 and 5,770,321. The BOC Group's well known SuperE-III and Super-E IV coatings are generally referenced in U.S. Pat. Nos.5,377,045 and 5,563,734 and exemplify such a known generic structure aswell.

[0010] In this respect the above-referenced '455 patent also achievedsome degree of matchability and heat treatability in certaincircumstances. Generally speaking, however, this body of prior art, as awhole, did not achieve the full degree of matchability and heattreatability desired for reliability in manufacturing while at the sametime achieving durability and the desirable substantially neutralblue-green color and low U-values and/or shading coefficients desired inI.G. units and laminates.

[0011] In view of the above it is apparent that there exists a need inthe art for a new layer coating system which is of a commerciallyacceptable color and which is also heat treatable as well as matchablewhen used in articles employing two or more light transmitting glasssubstrates in light transmitting relationship one with the other.

[0012] It is a purpose of this invention to fulfill this and other needsin the art which will become more apparent to the skilled artisan oncegiven the following disclosure.

SUMMARY OF THE INVENTION

[0013] This invention, generally speaking fulfills the above-describedneeds in the art by providing certain articles which include two or moreglass structures in light transmittance communication with each otherand which have a unique layer system of this invention on at least oneof its surfaces. In addition, this invention further provides a methodof making such articles. In this respect then, this invention provides:

[0014] In a glass article having at least two glass substrates in lighttransmitting communication with each other and having a sputter coatedheat treatable layer system on at least one of said substrates, whichcoated substrate is heat treated, the improvement comprising said glassarticle being matchable and wherein said sputter coated layer systemcomprises from the glass substrate on which it is coated, outwardly:

[0015] a) a layer of silicon nitride;

[0016] b) a substantially metallic layer of nickel or nickel alloyhaving a nickel content of at least about 10% by weight Ni, this layerbeing substantially free of a nitride or oxide of said metal;

[0017] c) a substantially metallic layer of silver;

[0018] d) a substantially metallic layer of nickel or a nickel alloyhaving a nickel content of at least about 10% by weight Ni, this layerbeing substantially free of a nitride or an oxide of said metal; and

[0019] e) a layer of silicon nitride; wherein said heat treated layercoating system has a visible transmittance at least about 4% greaterthan before it was heat treated, and wherein the relative thicknesses ofsaid layers combine to result in said heat treated coated substratewhich when viewed monolithically from the glass side of said coating hasa ΔE*_(ab) no greater than 5.0 and a Δa* less than 0.8.

[0020] In another aspect of this invention there is provided, in themethod of making a matchable glass article having at least two glasssubstrates in light transmitting communication with each other andhaving a heat treatable sputter coated layer system on at least onesurface of a said substrate which coated substrate is heat treated, theimprovement comprising the steps of:

[0021] a) sequentially sputter coating onto a surface of at least one ofthe glass substrates a said heat treatable layer system which comprisesfrom the glass substrate on which it is coated, outwardly:

[0022] a layer of silicon nitride;

[0023] a substantially metallic layer of nickel or nickel alloy having anickel content of at least about 10% by weight Ni, this layer beingsubstantially free of a nitride or oxide of said metal;

[0024] a substantially metallic layer of silver;

[0025] a substantially metallic layer of nickel or a nickel alloy havinga nickel content of at least about 10% by weight Ni, this layer beingsubstantially free of a nitride or an oxide of said metal; and

[0026] a layer of silicon nitride; wherein the relative thicknesses ofsaid layers combine to result in said article when viewed from a glassside having a ΔE*_(ab) no greater than 3.0 and a Δa* less than 0.7;

[0027] b) subjecting said substrate having said coating thereon to aheat treatment which increases the visible transmittance of said coatedsubstrate by at least about 4%; and

[0028] c) thereafter fabricating said glass substrates so as to be inlight transmitting communication with each other thereby to form saidmatchable glass article.

[0029] In certain preferred embodiments the desired color issubstantially neutral but preferably is located in the blue-greenquadrant as represented by both a* and b* being negative. In furtherpreferred embodiments of this invention the glass article is a window ordoor formed from at least two sheets of glass and fabricated as eitheran I.G. unit or a glass laminate. In this respect the heat treatmentemployed in the preferred embodiments of this invention is selected frombending, tempering, or heat strengthening, and most preferably istempering.

[0030] This invention will now be described with respect to certainembodiments thereof as illustrated in the following drawings, wherein:

IN THE DRAWINGS

[0031]FIG. 1 is a partial side sectional view of an embodiment of alayer system according to this invention.

[0032]FIG. 2 is a partial cross-sectional view of an I.G. unit ascontemplated by this invention.

[0033]FIG. 3 is a partial schematic perspective view of a houseemploying as a window, door and wall an I.G. unit and laminate accordingto this invention.

[0034]FIG. 4 is a partial cross-sectional schematicized view of anembodiment of an I.G. unit in pre-fabrication stage.

[0035]FIG. 5 is a partial cross-sectional schematicized view of a bentlaminate as contemplated by this invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0036] Certain terms are prevalently used in the glass coating art,particularly when defining the properties and solar managementcharacteristics of coated glass. Such terms are used herein inaccordance with their well known meaning. For example, as used herein:

[0037] Intensity of reflected visible wavelength light, i.e.“reflectance” is defined by its percentage and is reported as R_(x)Y(i.e. the Y value cited below in ASTM E-308-85), wherein “X” is either“G” for glass side or “F” for film side. “Glass side” (e.g. “G”) means,as viewed from the side of the glass substrate opposite that on whichthe coating resides, while “film side” (i.e. “F”) means, as viewed fromthe side of the glass substrate on which the coating resides.

[0038] Color characteristics are measured and reported herein using theCIE LAB 1976 a*, b* coordinates and scale (i.e. the CIE 1976 a*b*diagram). Other similar coordinates may be equivalently used such as bythe subscript “h” to signify the conventional use of the Hunter method(or units) Ill. C, 10° observer, or the CIE LUV u*v* coordinates. Thesescales are defined herein according to ASTM D-2244-93 “Standard TestMethod for Calculation of Color Differences From Instrumentally MeasuredColor Coordinates” Sep. 15, 1993 as augmented by ASTM E-308-85, AnnualBook of ASTM Standards, Vol. 06.01 “Standard Method for Computing theColors of Objects by Using the CIE System” and/or as reported in IESLIGHTING HANDBOOK 1981 Reference Volume.

[0039] The terms “emissivity” and “transmittance” are well understood inthe art and are used herein according to their well known meaning. Thus,for example, the term “transmittance” herein means solar transmittance,which is made up of visible light transmittance (TY), infrared energytransmittance, and ultraviolet light transmittance. Total solar energytransmittance (TS) is then usually characterized as a weighted averageof these other values. With respect to these transmittances, visibletransmittance, as reported herein, is characterized by the standardIlluminant C technique at 380-720 nm; infrared is 800-2100 nm;ultraviolet is 300-400 nm; and total solar is 300-2100 nm. For purposesof emissivity, however, a particular infrared range (i.e. 2,500-40,000nm) is employed.

[0040] Visible transmittance can be measured using known, conventionaltechniques. For example, by using a spectrophotometer, such as a Beckman5240 (Beckman Sci. Inst. Corp.), a spectral curve of transmission isobtained. Visible transmission is then calculated using the aforesaidASTM 308/2244-93 methodology. A lesser number of wavelength points maybe employed than prescribed, if desired. Another technique for measuringvisible transmittance is to employ a spectrometer such as a commerciallyavailable Spectrogard spectrophotometer manufactured by PacificScientific Corporation. This device measures and reports visibletransmittance directly. As reported and measured herein, visibletransmittance (i.e. the Y value in the CIE tristimulus values, ASTME-308-85) uses the Ill. C., 10° observer.

[0041] “Emissivity” (E) is a measure, or characteristic of bothabsorption and reflectance of light at given wavelengths. It is usuallyrepresented by the formula:

E=1−Reflectance_(film)

[0042] For architectural purposes, emissivity values become quiteimportant in the so-called “mid-range”, sometimes also called the “farrange” of the infrared spectrum, i.e. about 2,500-40,000 nm., forexample, as specified by the WINDOW 4.1 program, LBL-35298 (1994) byLawrence Berkeley Laboratories, as referenced below. The term“emissivity” as used herein, is thus used to refer to emissivity valuesmeasured in this infrared range as specified by the 1991 Proposed ASTMStandard for measuring infrared energy to calculate emittance, asproposed by the Primary Glass Manufacturers' Council and entitled “TestMethod for Measuring and Calculating Emittance of Architectural FlatGlass Products Using Radiometric Measurements”. This Standard, and itsprovisions, are incorporated herein by reference. In this Standard,emissivity is reported as hemispherical emissivity (E_(h)) and normalemissivity (E_(n)).

[0043] The actual accumulation of data for measurement of suchemissivity values is conventional and may be done by using, for example,a Beckman Model 4260 spectrophotometer with “VW” attachment (BeckmanScientific Inst. Corp.). This spectrophotometer measures reflectanceversus wavelength, and from this, emissivity is calculated using theaforesaid 1991 Proposed ASTM Standard which has been incorporated hereinby reference.

[0044] Another term employed herein is “sheet resistance”. Sheetresistance (R_(s)) is a well known term in the art and is used herein inaccordance with its well known meaning. It is here reported in ohms persquare units. Generally speaking, this term refers to the resistance inohms for any square of a layer system on a glass substrate to anelectric current passed through the layer system. Sheet resistance is anindication of how well the layer is reflecting infrared energy, and isthus often used along with emissivity as a measure of thischaracteristic. “Sheet resistance” is conveniently measured by using a4-point probe ohmmeter, such as a dispensable 4-point resistivity probewith a Magnetron Instruments Corp. head, Model M-800 produced bySignatone Corp. of Santa Clara, Calif.

[0045] “Chemical durability” or “chemically durable” is used hereinsynonymously with the term of art “chemically resistant” or “chemicalstability”. Chemical durability is determined by boiling a 2″×5″ sampleof a coated glass substrate in about 500 cc of 5% HCl for one hour (i.e.at about 220° F.). The sample is deemed to pass this test (and thus thelayer system is “chemically resistant” or is deemed to be “chemicallydurable” or to have “chemical durability”) if the sample's layer systemshows no visible discoloration or no pinholes greater than about 0.003″in diameter after this one hour boil.

[0046] “Mechanical durability” as used herein is defined by either oneof two alternative tests. The first test uses a Pacific ScientificAbrasion Tester (or equivalent) wherein a 2″×4″×1″ nylon brush iscyclically passed over the layer system in 500 cycles employing 150 gmof weight, applied to a 6″×17″ sample. In this test, if no substantial,noticeable scratches appear when viewed with the naked eye under visiblelight, the test is deemed passed, and the article is said to be“mechanically durable” or to have “mechanical durability”.

[0047] Thicknesses of the various layers in the systems reported aremeasured by, and thus the term, “thickness” as used herein is definedby, alternative techniques. In one technique, known optical curves, or,in the alternative, the use of conventional needle profilometery isemployed. In another and particularly advantageous technique, anmulti-wavelength, variable angle spectrophotometric ellipsometer made byJ. A. Woollam Co., Lincoln, Nebr., is used.

[0048] The term “U-value” (synonymous with “thermal transmittance”) is aterm well understood in the art and is used herein according to thiswell known meaning. “U-value” herein is reported in terms ofBTU/hr/ft²/° F., and may be determined according to the guarded hot boxmethod as reported in, and according to ASTM designation: C236-89(reapproved 1993).

[0049] The term “shading coefficient” is a term well understood in theart and is used herein according to its well known meaning. It isdetermined according to ASHRAE Standard 142 “Standard Method forDetermining and Expressing the Heat Transfer and Total OpticalProperties of Fenestration Products” by ASHRAE Standards ProjectCommittee, SPC 142, September 1995.

[0050] In order to properly employ the term “heat treatable” (or itssynonym “heat treatability”) when used as a characteristic of thisinvention, it must be defined more narrowly than heretofore employed inthe prior art as represented by the aforesaid '585 patent. Here, as inthe prior art, the term continues to refer to the ability of the coatedlayer system to withstand the type of heat treatment to which it issubjected without adverse affect upon its required characteristics.However, to be “heat treatable” (or to have “heat treatability”) for thepurposes of this invention, the heat treatment to which the layercoating system is subjected must also increase visible transmittance byat least about 4% and preferably by about 5-7%. It is a finding of thisinvention that this increase is important in order to achieve“matchability” or to be “matchable” as these two terms are employedherein for most of the layer systems contemplated herein.

[0051] Provided that the heat treatment results in this increasedvisible transmittance, then, in all other respects the definition of“heat treatable” and “heat treatability” remains the same as heretoforeemployed in the art (e.g. as in the '585 patent referenced above). Forexample, such heat treatments as generally contemplated herein may beany process which employs relatively high temperatures and which in thenormal circumstance would adversely affect most prior art coatings. Suchheat treatments include tempering, bending, heat strengthening andcertain processes used to form I.G. units or glass laminates whichemploy high sealing or fabricating temperatures. Such heat treatments,e.g. tempering and bending, often necessitate heating the coatedsubstrate to temperatures above 1100° F. (593° C.) and up to 1450° F.(788° C.) for a sufficient period of time to insure the end result.

[0052] Tolerable, so as to be included within the definition of “heattreatable”, are changes for the better in the layer system resultingfrom the heat treatment employed. In addition to increased visibletransmittance, such heat treatments for example, may beneficially resultin lower emissivity and sheet resistance values. Such beneficial changesdo not render the layer systems of this invention nonheat treatable. Formost commercial purposes, for example, an emissivity change for thebetter (i.e. lowering of the E value) due to the heat treatment is notonly tolerated but desirable because it does not affect visualappearance and thus matchability, although it is normally important thatthe change take place uniformly across the substrate and is independentof the parameters used to perform the heat treatment.

[0053] The term “matchable” and its definition as used herein, thenfollows from the term (and definition above, of) “heat treatable”. Ascontemplated by this invention the term “matchable” simply means that aglass article having at least two glass substrates in lighttransmittance relationship with each other, wherein at least one of theglass substrates has a sputter coated layer coating system of thisinvention on it, will appear to the naked human eye to looksubstantially the same when comparing its unheat treated appearance toits appearance after heat treatment, at least when viewed from theso-called glass side (i.e. looking through at least one substrate ofglass before viewing the coating).

[0054] The glass articles contemplated by this invention are notmonolithic glass sheets. Rather as described above, they are articleswhich comprise at least two glass substrates (e.g. sheets) which are inlight transmitting (and thus reflecting) relationship with one another.The usual form of such an article is, of course, an I.G. unit orlaminate.

[0055] While the coating systems of this invention are monolithicallyheat treatable, they need not be and often are not, monolithicallymatchable. In fact many systems herein contemplated only achievematchability when used in a dual or multi-glass substrate structure asdescribed. While the precise reason for this may not be fullyunderstood, it is believed, and thus is a finding of this invention,that by using two or more glass substrates located in transmitting (andthus reflecting) relationship with one another, the reflection ofvisible light from the glass substrate opposite the viewed substratetends to mask or cancel any difference in appearance between the heattreated, coated substrate being viewed when compared to its unheattreated counterpart. It is further believed that when the lighttransmittance of the coatings of this invention increase during heattreatment, this enhances the aforesaid masking affect, thus furthercancelling any difference.

[0056] It, therefore, becomes an unexpected beneficial characteristic ofthis invention due to this masking effect, that, as aforesaid, the heattreated coated substrate if employed monolithically, i.e. compared toitself when unheat treated, need not be matchable in order to achievematchability in the articles of this invention. This, in turn, createsthe substantial benefit of not imposing upon the heat treated substratethe heretofore believed necessary characteristic of having to employ aΔE less than 2.0. Rather, as described below the ΔE of the monolithic(individual) substrate may be substantially higher than 2.0 andmatchability still be achieved in the dual or multipane articles of thisinvention.

[0057] It is a still further finding of this invention for the articlesand systems herein contemplated that matchability is best definable byreference to certain characteristics in addition to ΔE. It has now beensurprisingly found, in fact, that for matchability of the systemsherein, a limit upon Δa* should be defined. Preferably, and optionally,the color may also be defined to maximize the degree of matchabilityachieved. This color, of course, may be conveniently described byreference to the aforesaid conventional a*, b* values, which for thepurposes of this invention, to maintain the color in the desiredsubstantially neutral color range tending to the blue-green quadrant,should both be negative. If the color desired is different, then thea*b* values will change accordingly to meet the customer's needs whilestill maintaining matchability through the appropriate selection of aparticular ΔE and Δa*.

[0058] Closely related to the above findings is the still furtherfinding of this invention that in achieving matchability for anyparticular layer system herein, particularly if colors other thanrelatively neutral blue-green are desired, that the following generalguidelines be followed:

[0059] a) the range of ΔE needed to insure matchability generally variesdepending upon the color quadrant in which the color resides; and

[0060] b) the so-called b* component when defining the color by its a*b*coordinates is less important to control than is the a* component, andthus Δa*.

[0061] The term “delta E” (i.e. “ΔE”) is well understood in the art andis reported, along with various techniques for determining it, in theaforesaid ASTM-2244-93 as well as being reported in Hunter et al, TheMeasurement of Appearance, 2nd Ed. Cptr. Nine, p162 et seq. [John Wiley& Sons, 1987].

[0062] As used in the art, “ΔE” is a way of adequately expressing thechange (or lack thereof) in reflectance and/or transmittance (and thuscolor appearance, as well) in an article. ΔE may be calculated by the“ab” technique, by the Hunter technique (designated by employing asubscript “H”) and/or by the Friele-MacAdam-Chickering (FMC-2)technique. All are deemed useful, and equivalent for the purposes ofthis invention. For example, as reported in Hunter et al referencedabove, the rectangular coordinate/scale technique (CIE LAB 1976) knownas the L*, a*, b* scale may be used, wherein:

[0063] L* is (CIE 1976) lightness units

[0064] a* is (CIE 1976) red-green units

[0065] b* is (CIE 1976) yellow-blue units

[0066] and the distance ΔE between L*_(o) a*_(o) b*_(o) and L*₁ a*₁ b*₁is the rectangular coordinates:

ΔE*_(ab)=[(ΔL*)²+(Δa*)²+(Δb*)²]^(½)

[0067] where:

[0068] ΔL*−L*₁−L*_(o)

[0069] Δa*=a*₁−a*_(o)

[0070] Δb*=b*₁−b*_(o)

[0071] In this technique, as used in this invention, the subscript “o”represents the coating (coated article) before heat treatment and thesubscript “1” represents the coating (coated article) after heattreatment.

[0072] When hereinafter, and in the claims, the term ΔE is quantified,the numbers employed are those calculated by the aforesaid (CIE LAB1976) L*, a*,b* coordinate technique and thus ΔE is recited as ΔE*_(ab).However, within the scope of this invention and the quantification of ΔEare, of course, the equivalent numbers if converted to those calculatedby any other technique employing the same concept of ΔE as definedabove.

[0073] As a general guideline, in this respect, then, it has been foundthat, for the layer systems as contemplated by this invention, when thecoated monolithic glass substrate has a color before heat treatmentfalling within the following range: General (about) Preferred (about) a*−2.6 to −6.0 −3.6 to −5.0 b* −3.5 to −9.5 −5.5 to −7.5

[0074] “matchability” (i.e. to be “matchable”) is usually achieved inarticles of this invention when viewed from the glass side if the heattreatment results in an increase in visible light transmittance of atleast about 4% and preferably about 5-7% and if monolithically: General(about) Preferred ΔE*_(ab) is <5.0 <4.0 Δa* is <0.8 <0.5

[0075] A ΔE*_(ab) and Δa* of zero is, of course, the ideal situationwhich the skilled artisan should strive for.

[0076] The term “about” is used in the above ranges and hereingenerally, to take into account minor variations that may occurdepending upon the precise layer system employed, the somewhatsubjective nature of the human eye and in recognition of the fact thatthe definition of “matchable” is similarity of appearance to the nakedeye for the purpose intended, as well as the understanding that ΔE andΔa* are scientific techniques for describing this concept as it relatesto the human eye.

[0077] As a further guideline, and due to the above-described maskingeffect of appropriately positioned glass substrates as contemplatedherein, a monolithic sheet provided with a coating of this invention andemployed as one of two or more substrates in the articles hereincontemplated, may now have a ΔE greater than hereinbefore thoughttolerable for matchability. In fact it has been surprisingly found thatthe monolithic heat treatable coated glass sheet need only have aΔE*_(ab) less than about 5.0 and preferably less than about 4.0 toobtain matchability in the final product. Moreover, as a further generalguideline, the corresponding Δa* in this sheet need only be less thanabout 0.8 and preferably less than about 0.5.

[0078] Turning now to FIG. 1, there is illustrated a partialcross-sectional view of a typical embodiment of a heat treatable glasssubstrate having a sputter coated layer system thereon according to thisinvention. Therein glass substrate 1 has provided on it an undercoat 3of Si₃N₄, a first intermediate layer 5 of a non-nitrided and nonoxidizednickel or nickel alloy (preferably a nichrome of, by weight percent,80/20 nickel), an infrared energy reflecting layer 7 of silver, a secondintermediate layer 9 of a non-nitrided and nonoxidized nickel or nickelalloy (preferably a nichrome of, by weight percent, 80/20nickel/chromium) and a top layer 11 of Si₃N₄.

[0079] The thicknesses of these layers may vary and in this respectuseful ranges thereof for certain embodiments are given below. It isunderstood that it is, generally speaking, the relative thicknesses ofthe system, which in general are chosen to achieve the desired resultsherein.

[0080] While the layer systems of this invention find use in theautomotive window and windshield arts, they are particularly useful assolar management coatings in the so-called architectural field (i.e.windows and doors for building structures such as office buildings,apartments, and residential houses). When so employed in thearchitectural field, they are employed, normally but not necessarily fortheir matchability in multi-pane insulating glass units (“I.G. units”)such as of the type illustrated in FIGS. 2 and 4, or as doors andwindows in residential homes as illustrated in FIG. 3, or as inlaminates as illustrated in FIG. 5.

[0081]FIG. 3 is a schematic view of a typical family dwelling 28 havingvarious portals in which the subject invention may be employed. Forexample, an unheat treated window 30 may employ as a “storm window” ornoise abating system, an I.G. unit of this invention such as isillustrated in FIG. 2. Sliding door 50 or non-sliding glass door panel52 as well as front door panel 54 may be so constructed by employingthis invention as a heat treated I.G. unit. This requires thatmatchability be achieved between the heat treated and unheat treatedwindows/doors for obvious aesthetic reasons. Matchability, of course, ishere achieved by the use of layer system 24 according to this invention.

[0082] With reference to FIG. 2, there is illustrated, somewhatschematically, a typical I.G. unit in accordance with this invention. Inorder to differentiate the “inside” of the I.G. unit (labelled “In”)from its “outside” (labelled “Out”), the sun 19 is schematicallypresented. As can be seen, such an I.G. unit is made up of “outside”glass pane (sheet) 21 and “inside” glass pane (sheet) 23. These twoglass panes (e.g. float glass of 2 mm-8 mm thick) are sealed at theirperipheral edges by a conventional sealant 25 and are provided with aconventional desiccant strip 27. The panes are then retained in aconventional window or door retaining frame 29 (shown in partialschematic form). By sealing the peripheral edges of the glass sheets andreplacing the air in chamber 30 with a gas such as argon, a typical,high insulating value I.G. unit is formed. Chamber 20 in this respect istypically about ½″ in width. Either inner wall 24 or 26 (or both) may beprovided with a layer system of this invention. As illustrated, innerwall 24 of outside glass sheet 21 in this embodiment, has been providedwith a sputter-coated layer coating system 22 applied thereto usingconventional sputter coating techniques. As can be seen, such a systemeffectively includes the “masking” principle discovered as a part ofthis invention since, for example, an observer of the home from theoutside will look through pane 21, coating 24, space 30 and pane 23.However, in doing so, because some of the sunlight passing through pane21 and striking pane 23 is reflected back from pane 23, reaching theobserver's eye, the masking effect helps to neutralize any smalldifference that might have otherwise existed (e.g. if the windows/doorswere monolithic sheets) thereby to create the desired matchability.

[0083] Attention is now directed to FIG. 4 wherein there isschematically illustrated a typical two-pane I.G. unit stack prior tosealing. In the I.G. unit of FIG. 4, the prestack employs two typical,clear float glass sheets 31 and 33 separated a selected distance (e.g.0.1 mm) by glass beads 35. Lower sheet 33, of slightly larger size thanupper sheet 31, has a layer system 37 according to this inventionsputter coated by conventional techniques onto its inner planar surface34. Optionally, the inner planar surface 32 of sheet 31 may be used forthe layer coating, or both surfaces 32 and 34 may be so employed. Aconventional sealant 39 (e.g. a relatively low melting ceramic) is thenprovided in the peripheral area 41 defined by centering the smallersheet 31 on the larger sheet 33.

[0084] In conventional fashion, sufficient heat is then applied so as tocause sealant 39 to flow and seal the two sheets together thereby tocreate an insulating chamber 43. Thereafter, after cool down, a vacuumis applied to remove as much air and water vapor as is economicallyfeasible, and optionally to either leave a vacuum or replace the air andwater vapor with an inert gas such as Argon. In an alternative techniquethe edges of the glass are flame sealed, rather than using a sealant. Ineither instance, heat must be applied to create the seal and drive offthe water vapor. Thus the heat treatable embodiments of this inventionfind unique applicability in I.G. units of the type shown in FIG. 4wherein the layer system must be able to withstand the heat employedduring sealing without adversely affecting its desired characteristics.

[0085] In yet another alternative, a vacuum process is not employed anda spacing of ½″ for the chamber is effected by various known,conventional techniques. In such a process the insulating chamber isusually filled with Argon so as to displace the air and any water vapor(i.e. humidity or moisture) that might be present. In both situationsthe use of two (or more, if tri-pane I.G.'s are built) sheets,positioned in light transmitting relationship one with respect to theother, brings into being the masking effect such that the I.G. unit ismatchable even if, monolithically, pane 21 is not, due to too high ΔE.

[0086] In this respect, the term “heat treatable” as used hereinincludes those I.G. unit sealing techniques which employ sufficientlyhigh temperatures that would normally adversely affect or destroy aconventional layer system, but does not include those sealing techniqueswhich employ such low temperatures so as to not affect virtually allcoatings used for this purpose.

[0087] When forming most I.G. units, multiple “handling” steps are oftenrequired, thus necessitating a layer system which is mechanicallydurable. Moreover, due to the nature of the process and materialsemployed, chemical durability is required. The preferred embodiments ofthe layer systems of this invention achieve both chemical and mechanicaldurability, thus making them particularly useful in forming I.G. unitshaving excellent U-values and other solar management properties, whileat the same time being matchable.

[0088] The preferred processes and apparatus used to form the layercoating systems of this invention may be any known, conventionalsputter-coating system. An example of such systems are the multi-chambersystems produced by Airco, Inc., such as the G-49 large area flat glasssputter coater made by this company. It is to be noted here that it isan aspect of this invention that its unique results are achieved throughthe use of conventional sputter-coating techniques without the need forspecial processes to relieve intrinsic stresses as reported in U.S. Pat.No. 5,377,045.

[0089] Attention is now directed to FIG. 5 which, in partialcross-sectional form, illustrates a typical bent laminate 60 accordingto this invention. It is understood, of course, that laminate 60 neednot be bent, i.e. it could be flat. Since laminate 60 is bent, however,it often will be required to be matchable with its unbent counterpart,such as in the case where it is used as a bent skylight in house 28 (notshown), which then must match with windows and doors 50, 52, etc. whichmay themselves be bent or flat (as illustrated).

[0090] Laminate 60 includes two panes of clear glass 62, 64respectively, which are sealed together in conventional fashion. Eitheror both of the inner facial surfaces of panes 62, 64 have, beforefabrication and bending, sputter coated thereon a layer system 66according to this invention. The laminate is then constructed and bent,as by heat slumping at the slumping temperature of the glass on a formsled or cradle (sometimes referred to as a “coffin”) in conventionalfashion to form the curved laminated article which thereafter may beprovided with a conventional frame member (not shown for convenience).During bending, the transmittance of the coated pane(s) increases by atleast about 4% to insure matchability.

[0091] As can be seen, pane 62 and pane 64 are positioned to be in lighttransmitting relationship one to the other. Therefore, no matter whichside (“A” or “B” in FIG. 5) of the laminate one views the structure fromthe masking effect of reflection from the pane opposite the viewer (e.g.pane 62 if the viewer is on side “B” helps achieve matchability of theunit although the pane(s) with the coating on it, by itself, is notnecessarily matchable, although it may be. Preferably only one pane iscoated, the other being uncoated. It is also considered a part of thisinvention that more than two substrates may be present in the laminate,as well as that at least one of them may be tempered or heatstrengthened, as well as bent.

[0092] As illustrated in FIG. 1, the substrate 1 is preferably glass oran equivalent and the preferred layer systems of this invention consistessentially of five (5) layers. While other layers may be employed, theymust not significantly detract from the characteristic of at least“matchability” herein achieved by these five layers. With reference tothe numerals in FIG. 1, the following range of thicknesses have beenfound to be desirable for insuring the achievement of “matchability” andheat treatability, and in most instances the other characteristics aswell, as noted below. “About” Preferred Layer No. Thickness (Å)Thickness (Å) 3 310-350 330  5 10-20 13 7 52-62 57 9 10-20 12 11 390-440 410 

[0093] With regard to layers 3 and 11 which consist essentially ofSi₃N₄, the target of Si employed to form this layer system (in anitrogen environment as known in the art) may be admixed with up to 6%by weight aluminum or stainless steel (e.g. SS#316), with about thisamount then appearing in the layer so formed. While layers 5 and 9 maybe metallic nickel, a nichrome preferably consisting essentially of, byweight about 80-90% Ni and 10-20% Cr, may be employed. Moreover, whileit is perhaps possible to employ certain other IR reflecting metals aslayer 7, such as gold or platinum, the preferred layer 7 herein consistsessentially of metallic silver, the others being considered a lessdesirable equivalent so long as they achieve the desired result.

[0094] An example of layers 5 and 9 include not only SS-316 whichconsists essentially of 10% Ni and 90% other ingredients, mainly Fe andCr, but Haynes 214 alloy as well, which by weight consists essentiallyof (as a nominal composition): Element Weight % Ni 75.45 Fe  4.00 Cr16.00 C  .04 Al  4.50 Y  .01

[0095] It is believed important to the achievement of maximized chemicaldurability that layers 5 and 9 include at least 10% by weight nickel,and that these layers be present in substantially unoxidized form (orhave undergone only a minor amount of oxidation) and are preferably,substantially free of a nitride of the nickel or chromium or othermetallic elements employed.

[0096] For most embodiments contemplated by this invention, thefollowing characteristics will be present in a monolithic glass sheetuseful in an I.G. unit to create matchability when using the layersystem above-described, sputter coated onto one of its flat surfaceswithin the range of thicknesses as set forth above. The characteristicsreported are based upon a glass substrate formed of clear, conventionalfloat glass (i.e. made by the conventional float process) having athickness of 6 mm. For glasses of different thicknesses or if colored,certain thickness dependent characteristics as known in the art, willchange accordingly. MONOLITHIC SHEET (6 mm THICK) PREFERRED SPECIFICCHARACTERISTIC RANGE RANGE EXAMPLE TY (%) before h.t. 63-73 67-72 70after h.t. 68-78 72-77 75 R_(G)Y (%) before h.t.  7-13  8-12 10 afterh.t.  7-13  8-12 8 a* before h.t. −2.6 to −6.0 −3.6 to −5.0 −4.3 afterh.t. −2.3 to −6.3 −3.3 to −5.3 −4.3 b* before h.t. −3.5 to −9.5 −5.5 to−7.5 −6.5 after h.t.  −4.5 to −10.5 −6.4 to −9.0 −7.7 R_(f)Y (%) beforeh.t. 3-7 4-6 5.0 after h.t.   2-6.4   3-5.4 4.2 a* before h.t. +1.4 to−3.4 +0.4 to −2.4 −1.0 after h.t. −0.6 to −6.0 −1.6 to −5.0 −3.3 b*before h.t. +2.5 to −6.5 +0.5 to −4.5 −2.0 after h.t.  −3 to −12  −5.0to −10.0 −7.5 E_(n) before h.t. 0.16-0.25 0.18-0.22 0.20 after h.t.0.18-0.23 0.16-0.20 0.18 E_(h) before h.t. 0.17-0.26 0.19-0.23 0.21after h.t. 0.15-0.24 0.17-0.21 0.19 R_(g) (ohms/sq) before h.t. 15-2015.5-18.5 17.0 after h.t. 10-20 11.5-14.5 13.0 ΔE*_(ab) <5.0  <4.0 3.6Δa* <0.8 <0.5 0.0

[0097] In the above table, TY is visible transmittance, “h.t.” meansheat treatment (here tempering), RY is reflectance, subscript “f” meansfilm side (i.e. coating side) and subscript “G” means glass side. The a*and b* numbers are the color coordinates as measured according to theabove-described CIE LAB 1976, Ill.C.10° observer technique, E_(n) isnormal emissivity, E_(h) is hemispherical emissivity and R_(s) is sheetresistance, here reported in ohms per square, ΔE*_(ab) and Δa* are hereused as defined above.

[0098] As can be seen in the specific example given in the above table,ΔE*_(ab) is 3.6. Even though Δa* is a very acceptable 0.0, this ΔE valueis too large for the monolithic sheet to itself achieve matchability(i.e comparing its heat treated form to its unheat treated form,monolithically). However, when this specific example is employed in anI.G. unit or laminate, the difference between the heat treated form andunheat treated form is masked and the two ultimate products arematchable.

EXAMPLE NO. 2

[0099] As another example of the heat treatability and matchability ofthe subject invention, another sheet of 6 mm clear float glass is coatedwith a layer system according to this invention and cut so as to formtwo glass panes useful in two separate I.G. units of ½″ air gap eachemploying another annealed clear float glass sheet of 6 mm thickness.One of the coated cut sheets is then tempered in a conventionaltempering furnace at about 1265° F. for three minute cycles and quenchedto room temperature.

[0100] Coating layer thickness measurements are made according to theellipsometer (J. A. Woollam Co.) technique described above. The coateremploys five isolated coating zones, only three zones being used, inconventional fashion, and the operational setup for each is as follows:GENERAL SETUP Coat Zone CZ-1 CZ-2 CZ-3 CZ-4 CZ-5 Material Ti Ti Si* NiCrAg NiCr Si* Power Off Off On On On On On Gases Off Off On On On On OnLinespeed 200 in/min

[0101] COAT ZONE #1, PROCESS PARAMETERS: Cathode # 1 2 3 4 5 6 MaterialTi Ti Ti Ti Ti Ti Type C-Mag C-Mag C-Mag C-Mag C-Mag C-Mag Gas ArgonOxygen Nitrogen Flow, sccm 0 0 2000 Pressure 2.5 × 10-3 torr Power, kWOff Off Off Off Off Off Linespeed 200 in/min

[0102] COAT ZONE #2, PROCESS PARAMETERS: Cathode # 7 8 9 10 11 12Material Ti Ti Ti Ti Ti Ti Type C-Mag C-Mag C-Mag C-Mag C-Mag C-Mag GasArgon Oxygen Nitrogen Flow, sccm 0 0 1700 Pressure 2.5 × 10-3 torrPower, kW Off Off Off Off Off Off Linespeed 200 in/min

[0103] COAT ZONE #3, PROCESS PARAMETERS: Cathode # 13 14 15 16 17 18Material Si Si Si Si Si Si Type C-Mag C-Mag C-Mag C-Mag C-Mag C-Mag GasArgon Nitrogen Flow, sccm 950 1150 Pressure 2.5 × 10-3 torr Power, kW 24.2  24.2 24.2 24.2 24.2 24.2 Linespeed 200 in/min

[0104] COAT ZONE #4, PROCESS PARAMETERS: Cathode # 31 32 33 MaterialNiCr Ag NiCr Type Planar Planar Planar Gas Argon Total Flow, sccm 18141814 Setting  100 Pressure 2.5 × 10-3 torr Power, kW   4.6   4.0 4.25Linespeed  200 in/min

[0105] COAT ZONE #5, PROCESS PARAMETERS: Cathode # 25 26 27 28 29 30Material Si Si Si Si Si Si Type C-Mag C-Mag C-Mag C-Mag C-Mag C-Mag GasArgon Nitrogen Flow, sccm 900 1502 Setting  18 Pressure 2.5 × 10-3 torrPower, kW  30.0  30.0 30.0 30.0 30.0 30.0 Linespeed 200 in/min

[0106] With reference to FIG. 1, the above process results in a fivelayer coating system having the following layer thicknesses wherein:Layer No. in Drawing Thicknesses (approx) (Å)  3 (Si₃N₄) 310   5 (80/20,Ni/Cr) 13  7 (silver) 57  9 (80/20, Ni/Cr) 12 11 (Si₃N₄) 410 

[0107] and wherein layers 5 and 9 are substantially free of any oxide ornitride of Ni or Cr. The layer system is chemically and mechanicallydurable as these terms are defined above, both before and after heattreatment.

[0108] As aforesaid, the sheet so coated is cut to the requisite size.One cut section of the coated sheet is then fabricated into an I.G. unitas shown in FIG. 2 using conventional techniques and a known organicsealant. The space 30 is a nominal ½″ and the coating is on the insideof sheet 21 to form an unheat treated I.G. unit. The other cut sectionof the coated sheet is tempered as described above and similarlyfabricated as the first I.G. unit, but here to form a heat treated I.G.unit.

[0109] The monolithic glass sheet had the following optical performancecharacteristics. MONOLITHIC SHEET Before Heat After Heat CharacteristicTreatment Treatment ΔE*_(ab) Δa* TY 69.83 74.81 2.6  a* −1.73 −1.98 b*−2.10 −0.95 R_(G)Y 9.91 8.20 3.95 a* −4.58 −4.55 −.03 b* −6.21 −8.04R_(F)Y 4.67 4.03 5.50 a* −1.16 −3.10 b* −2.87 −7.65 R_(S) 16.3 12.9E_(n) 0.197 0.172 E_(h) 0.214 0.187

[0110] As can be seen the monolithic sheet has achieved heattreatability and low-E values as well as an acceptable blue-green color.The film side ΔE*_(ab) is quite high, but this is not the important sideto consider. Rather, it is the glass side characteristic ΔE*_(ab) whichis important for matchability. Here the ΔE*_(ab) when viewed from theglass side is 3.95 while the Δa* is −0.03, and thus is not,monolithically, matchable. However, and noting the requisite increase invisible transmittance TY that has taken place, the I.G. units formed arematchable as demonstrated in the following chart: I.G. UNIT Unheat HeatTreated Treated Characteristic I.G. Unit I.G. Unit ΔE*_(ab) Δa* Tvis61.68 65.96 2.47 a* −3.22 −3.52 b* −2.12 −1.11 R_(G) (vis) 13.93 12.631.76 a* −4.27 −4.31 −.04 b* −6.93 −8.13 R_(F) (vis) 11.65 11.62 2.11 a*−1.62 −1.97 b* −2.5 −4.58 T, uv 39 42 T, solar 42 44 R, solar 14 15U-value 0.35 0.34 (winter) U-value 0.38 0.37 (summer) Shading 0.59 0.60coefficient S.h.g.C 0.503 0.519 R.H.G. 122 126

[0111] This comparison demonstrates the efficacy of this invention. Notonly is matchability achieved, but commercial color and very acceptableU-values and shading coefficients are achieved as well, as will beclearly recognized by the skilled artisan when comparing this data toknown commercial demands.

[0112] As further demonstrated, by maintaining both ΔE*_(ab) and Δa*within the above-recited ranges, even though Δb* becomes relativelylarge, laminates and I.G. units are formed from coated monolithic sheetswhich themselves, while heat treatable, may not be matchable, and yetthe I.G. unit and laminate is indeed very matchable. Moreover, theadvantages of silver are now present in the ultimate product resultingin very acceptable U-values and shading coefficients. As still furtherdemonstrated, a substantially neutral blue-green color, desirable formost architectural purposes is achieved because a* and b* are both keptin the negative.

[0113] Once given the above disclosure many other features,modifications and improvements will become apparent to the skilledartisan. Such other features, modifications and improvements aretherefore considered to be a part of this invention, the scope of whichis to be determined by the following claims:

We claim:
 1. In a glass article having at least two glass substrates inlight transmitting communication with each other and having a sputtercoated heat treatable layer system on at least one of said substrates,which coated substrate is heat treated, the improvement comprising saidglass article being matchable and wherein said sputter coated layersystem comprises from the glass substrate on which it is coated,outwardly: a) a layer of silicon nitride; b) a substantially metalliclayer of nickel or nickel alloy having a nickel content of at leastabout 10% by weight Ni, said layer being substantially free of a nitrideor oxide of said metal; c) a substantially metallic layer of silver; d)a substantially metallic layer of nickel or a nickel alloy having anickel content of at least about 10% by weight Ni, said layer beingsubstantially free of a nitride or oxide of said metal; and e) a layerof silicon nitride; wherein said heat treated layer coating system has avisible transmittance at least 4% greater than before it was heattreated; and wherein the relative thicknesses of said layers combine toresult in said heat treated coated substrate which when viewedmonolithically from the glass side of said coating has a ΔE*_(ab) lessthan 5.0 and a Δa* less than about 0.8.
 2. A glass article according toclaim 1 wherein said glass article is an insulating glass unit comprisedof two panes of glass in substantially spaced parallel position one withrespect to the other to define an insulating space therebetween, andwherein said layer coating system is located on a surface of one of saidpanes of glass within said insulating space.
 3. A glass articleaccording to claim 1 wherein said glass article is a glass laminatecomprised of at least two sheets of glass sealed together and havingtherebetween said layer coating system.
 4. A glass article according toclaim 1 wherein the thicknesses of the layers are within the followingrange: Layer Thickness (Å) a 310-350 b 10-20 c 52-62 d 10-20 e 390-440


5. A glass article according to claim 1 wherein said layer systemconsists essentially of said five layers and wherein a* and b* of saidcoated heat treated substrate are both negative.
 6. A glass articleaccording to claim 5 wherein said coated heat treated substrate has acolor wherein a* is from about −2.3 to −6.3 and b* is from about −4.5 to−10.5.
 7. A glass article according to claim 5 having a generallyneutral, blue-green color and wherein said coated heat treated substratehas a color wherein a* is from about −3.3 to −5.3 and b* is from about−6.4 to −9.0.
 8. A glass article according to claim 1 or 7 wherein saidheat treated coated glass substrate when viewed monolithically from theglass side of said coating has a ΔE*_(ab) of less than 4.0 and a Δa* ofless than 0.5.
 9. A glass article according to claim 1 wherein saidcoated heat treated glass substrate is comprised of a clear glasssubstrate.
 10. A glass article according to claim 1 wherein said coatedheat treated glass substrate is a tempered glass substrate having avisible transmittance after tempering which is 5-7% greater than beforetempering.
 11. A glass article according to claim 1 or 10 wherein saidglass article is an insulating glass unit and has a ΔE*_(ab) no greaterthan 3.0 and a Δa* less than 0.7 when viewed from a glass side.
 12. Aglass article according to claim 1 wherein said thicknesses of saidlayers are: Layer Thickness (Å) a 330  b 13 c 57 d 12 e 410 


13. A glass article according to claim 12 wherein said substantiallymetallic layers consist essentially of Ni, Fe, and Cr.
 14. A glassarticle according to claim 1 wherein said article is an insulating glassunit having an insulation space between said coated heat treated glasssubstrate and an uncoated glass substrate, wherein said glass of saidsubstrates is clear glass and wherein said heat treated coated glasssubstrate monolithically has the following characteristics before andafter heat treatment when measured at a glass thickness of 6 mm:Characteristic Range TY (%) before h.t. 63-73 after h.t. 68-78 R_(G)Y(%) before h.t.  7-13 after h.t.  7-13 a* before h.t. −2.6 to −6.0 afterh.t. −2.3 to −6.3 b* before h.t. −3.5 to −9.5 after h.t.  −4.5 to −10.5R_(f)Y (%) before h.t. 3-7 after h.t.   2-6.4 a* before h.t. +1.4 to−3.4 after h.t. −0.6 to −6.0 b* before h.t. +2.5 to −6.5 after h.t.  −3to −12 E_(n) before h.t. 0.16-0.25 after h.t. 0.18-0.23 E_(h) beforeh.t. 0.17-0.26 after h.t. 0.15-0.24 R_(S) (ohms/sq.) before h.t. 15-20after h.t. 10-20 ΔE*_(ab) <5.0 Δa* <0.8


15. A glass article according to claim 14 wherein said heat treatedcoated glass substrate monolithically has the following characteristicsbefore and after heat treatment when measured at a glass thickness of 6mm: Characteristic Range TY (%) before h.t. 67-72 after h.t. 72-77R_(G)Y (%) before h.t.  8-12 after h.t.  8-12 a* before h.t. −3.6 to−5.0 after h.t. −3.3 to −5.3 b* before h.t. −5.5 to −7.5 after h.t. −6.4to −9.0 R_(f)Y (%) before h.t. 4-6 after h.t.   3-5.4 a* before h.t.+0.4 to −2.4 after h.t. −1.6 to −5.0 b* before h.t. +0.5 to −4.5 afterh.t.  −5.0 to −10.0 E_(n) before h.t. 0.18-0.22 after h.t. 0.16-0.20E_(h) before h.t. 0.19-0.23 after h.t. 0.17-0.21 R_(S) (ohms/sq.) beforeh.t. 15.5-18.5 after h.t. 11.5-14.5 ΔE*_(ab) <4.0 Δa* <0.5


16. A glass article according to claim 14 wherein said insulating glassunit has the following characteristics when measured at a glasssubstrate thickness of 6 mm: Unheat Heat Characteristic Treated TreatedΔE*_(ab) Δa* Tvis 61.68 65.96 2.47 a* −3.22 −3.52 b* −2.12 −1.11 R_(G)(vis) 13.93 12.63 1.76 a* −4.27 −4.31 −.04 b* −6.93 −8.13 R_(F) (vis)11.65 11.62 2.11 a* −1.62 −1.97 b* −2.5 −4.58 T, uv 39 42 T, solar 42 44R, solar 14 15 U-value 0.35 0.34 (winter) U-value 0.38 0.37 (summer)Shading 0.59 0.60 coefficient

wherein “unheated” means an identical I.G. unit in which no coatedsubstrate in said article is heat treated and “heat treated” means thatsaid coated substrate is heat treated.
 17. A glass article according toclaim 16 wherein said heat treated coated glass substrate is tempered.18. A glass article according to claim 1 wherein the Δa* of said coatedglass substrate is substantially zero.
 19. In the method of making amatchable glass article having at least two glass substrates in lighttransmitting communication with each other and having a heat treatablesputter coated layer system on at least one surface of a said substratewhich coated substrate is heat treated, the improvement comprising thesteps of: a) sequentially sputter coating onto a surface of at least oneof said glass substrates a said heat treatable layer system whichcomprises from the glass substrate on which it is coated outwardly; afirst layer of silicon nitride; a second substantially metallic layer ofnickel or nickel alloy having a nickel content of at least about 10% byweight Ni, said layer being substantially free of a nitride or oxide ofsaid metal; a third substantially metallic layer of silver; a fourthsubstantially metallic layer of nickel or a nickel alloy having a nickelcontent of at least about 10% by weight Ni, said layer beingsubstantially free of a nitride or an oxide of said metal; and a fifthlayer of silicon nitride; wherein the relative thicknesses of saidlayers combine to result in said article when viewed from a glass sidehaving a ΔE*_(ab) no greater than 3.0 and a Δa* less than 0.7; b)subjecting said substrate having said coating thereon to a heattreatment which increases the visible transmittance of said coatedsubstrate by at least 4%; and c) thereafter fabricating said glasssubstrates so as to be in light transmitting communication with eachother thereby to form said matchable glass article.
 20. The methodaccording to claim 19 wherein said heat treatment is selected fromtempering, bending and heat strengthening.
 21. The method according toclaim 19 wherein said glass article is an insulating glass unitcomprised of two panes of glass one of said panes having said coatingthereon and said fabrication step includes retaining said panes insubstantially parallel relationship with each other thereby to define aninsulating space therebetween and wherein said layer coating system islocated on a surface of said coated pane which is located within saidinsulating space.
 22. The method according to claim 19 wherein saidarticle is a glass laminate comprised of at least two glass sheets, oneof which has said heat treatable sputter coated layer system thereon,and said fabrication step includes laminating said coated glass sheetafter it is heat treated to another glass sheet such that the saidcoating layer is located between said glass sheets.
 23. The methodaccording to claim 19 wherein the thicknesses of the layers are withinthe following range: Layer Thickness (Å) first 310-350 second 10-20third 52-62 fourth 10-20 fifth 390-440


24. The method according to claim 19 wherein said heat treatment istempering.
 25. The method according to claim 19 wherein said heattreatment increases said visible transmittance by 5%-7%.
 26. The methodaccording to claim 19 wherein said glass article has a generally neutralblue-green color and when viewed from the glass side of said coating hasa ΔE*_(ab) of less than 2.0 and a Δa* of less than 0.5.
 27. The methodaccording to claim 19 wherein said heat treatable coated glasssubstrate, monolithically when measured at a glass thickness of 6 mm hasa ΔE*_(ab) less than 5.0 and a Δa* less than 0.8.
 28. The methodaccording to claim 27 wherein said monolithic ΔE*_(ab) is less than 4.0and a Δa* is less than 0.5.
 29. The method according to claim 28 whereinsaid monolithic Δa* is substantially zero.
 30. The method of claim 19wherein said article is an insulating glass unit whose U-values andshading coefficients are substantially the same as those of an otherwiseidentically formed I.G. unit whose coated substrate is not heat treated.31. The method according to claim 30 wherein said U-values and shadingcoefficients are: I.G. Unit Unheated I.G. Unit Heat CharacteristicSubstrate Treated Substrate U-value (winter) 0.35 0.34 U-value (summer)0.38 0.37 shading coefficient 0.59 0.60


32. The method according to claim 19 wherein said layer coating systemso formed is mechanically and chemically durable both before and aftersaid heat treatment.
 33. A glass article according to claim 1, 4 or 12wherein said layer coating system so formed is mechanically andchemically durable both before and after said heat treatment.